U.S. patent application number 10/277397 was filed with the patent office on 2003-04-03 for systems and methods for controlling tissue ablation using multiple temperature sensing elements.
Invention is credited to Fleischman, Sidney D., Panescu, Dorin, Swanson, David K., Whayne, James G..
Application Number | 20030065322 10/277397 |
Document ID | / |
Family ID | 27403663 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030065322 |
Kind Code |
A1 |
Panescu, Dorin ; et
al. |
April 3, 2003 |
Systems and methods for controlling tissue ablation using multiple
temperature sensing elements
Abstract
Systems and associated methods place a temperature sensing
element in an "edge region" between an energy transmitting
electrode and a non-electrically conducting support body, where
higher temperatures are likely to exist. Reliable temperature
sensing, which is sensitive to variations in temperatures along the
electrode, results.
Inventors: |
Panescu, Dorin; (Sunnyvale,
CA) ; Fleischman, Sidney D.; (Menlo Park, CA)
; Whayne, James G.; (Saratoga, CA) ; Swanson,
David K.; (Mountain View, CA) |
Correspondence
Address: |
HENRICKS SLAVIN AND HOLMES LLP
SUITE 200
840 APOLLO STREET
EL SEGUNDO
CA
90245
|
Family ID: |
27403663 |
Appl. No.: |
10/277397 |
Filed: |
October 21, 2002 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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10277397 |
Oct 21, 2002 |
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09697895 |
Oct 26, 2000 |
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6500172 |
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09697895 |
Oct 26, 2000 |
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09154941 |
Sep 17, 1998 |
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6197021 |
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09154941 |
Sep 17, 1998 |
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08788782 |
Jan 24, 1997 |
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5810802 |
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08788782 |
Jan 24, 1997 |
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08439824 |
May 12, 1995 |
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08439824 |
May 12, 1995 |
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08286930 |
Aug 8, 1994 |
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08439824 |
May 12, 1995 |
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08287192 |
Aug 8, 1994 |
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Current U.S.
Class: |
606/41 ;
374/E1.005; 374/E3.009; 600/374; 606/31; 606/42 |
Current CPC
Class: |
A61B 2018/00821
20130101; A61L 29/145 20130101; A61B 5/287 20210101; A61B 2018/126
20130101; A61B 2018/128 20130101; A61L 31/145 20130101; A61B 18/12
20130101; A61B 2017/003 20130101; A61B 2017/00154 20130101; A61B
2018/00636 20130101; A61N 1/06 20130101; A61B 2018/00083 20130101;
A61B 2018/1467 20130101; G01K 1/026 20130101; A61B 2017/00092
20130101; A61B 2018/00791 20130101; A61B 5/6858 20130101; A61B
18/1206 20130101; A61B 2018/0066 20130101; A61B 18/20 20130101;
A61N 1/40 20130101; G01K 3/14 20130101; A61B 18/00 20130101; A61L
31/10 20130101; A61B 2017/00088 20130101; A61B 2018/0069 20130101;
A61B 18/1492 20130101; A61B 2018/00107 20130101; A61N 1/403
20130101; A61B 2018/0016 20130101; A61B 2018/00803 20130101; A61N
1/056 20130101; A61B 2018/00148 20130101; A61B 2018/1435 20130101;
A61B 2018/00101 20130101; A61B 2018/00797 20130101; A61B 2018/124
20130101 |
Class at
Publication: |
606/41 ; 606/42;
606/31; 600/374 |
International
Class: |
A61B 018/14 |
Claims
We claim:
1. A device for ablating body tissue comprising a support element
made of a material that does not conduct tissue ablation energy, an
electrode carried by the support element for contact with tissue,
the electrode being made of a material that transmits ablation
energy, the electrode having at least one edge that contacts the
material of the support element, and at least one temperature
sensing element carried by the electrode adjacent to the at least
one edge.
2. A device according to claim 1 and further including at least one
additional temperature sensing element carried by the electrode
away from the at least one edge.
3. A device for ablating body tissue comprising a support element
made of a material that does not conduct tissue ablation energy, an
electrode carried by the support element for contact with tissue,
the electrode being made of a material that transmits ablation
energy, the electrode having opposed edges that contact the
material of the support element, and temperature sensing elements
carried by the electrode adjacent to the opposed edges.
4. A device according to claim 3 and further including at least one
additional temperature sensing element carried by the electrode
away from the opposed edges.
5. A device according to claim 1 or 2 or 3 or 4 wherein the
electrode comprises a metallic material attached about the support
element.
6. A device according to claim 1 or 2 or 3 or 4 wherein the
electrode comprises wire wrapped about the support element.
7. A device according to claim 1 or 2 or 3 or 4 wherein the support
element is flexible and includes means for flexing the support
element.
8. A device according to claim 7 wherein the electrode is flexible
and flexes with the support element.
9. A device according to claim 1 or 2 or 3 or 4 wherein the
temperature sensing element comprises a thermistor.
10. A device according to claim 1 or 2 or 3 or 4 wherein the
temperature sensing element comprises a thermocouple.
11. A device according to claim 1 or 2 or 3 or 4 and further
including at least one additional temperature sensing element
carried by the support body.
12. A device for ablating body tissue comprising a support element
made of a material that does not conduct tissue ablation energy,
and an array of spaced apart electrodes carried by the support
element for contact with tissue, each electrode being made of a
material that transmits ablation energy, each electrode having
opposed edges that contact the material of the support element, and
at least one temperature sensing element carried by one of the
electrodes adjacent to at least one of its opposed edges.
13. A device according to claim 12 wherein each electrode carries
at least one temperature sensing element adjacent to at least one
of its opposed edges.
14. A device according to claim 12 wherein the array of electrodes
includes a first electrode that begins the array and a second
electrode that ends the array, and wherein both the first and
second electrodes carry at least one temperature sensing element
adjacent to at least one of its edges.
15. A device according to claim 14 wherein the array of electrodes
includes at least one intermediate electrode between the first and
second electrodes.
16. A device according to claim 15 wherein the at least one
intermediate electrode carries at least one temperature sensing
element adjacent to at least one of its edges.
17. A device according to claim 15 wherein the at least one
intermediate electrode carries at least one temperature sensing
element.
18. A device according to claim 12 wherein the support body carries
at least one temperature sensing element.
19. A device according to claim 12 wherein the at least one
electrode comprises a metallic material attached about the support
element.
20. A device according to claim 12 wherein the at least one
electrode comprises wire wrapped about the support element.
21. A device according to claim 12 wherein the support element is
flexible and includes means for flexing the support element.
22. A device according to claim 21 wherein the array of electrodes
is flexible and flexes with the support element.
23. A device according to claim 12 wherein the temperature sensing
element comprises a thermistor.
24. A device according to claim 12 wherein the temperature sensing
element comprises a thermocouple.
25. A system for ablating body tissue comprising a generator for
supplying ablation energy, a support element made of a material
that does not conduct ablation energy, an electrode carried by the
support element for contact with tissue, the electrode being made
of a material that transmits ablation energy, the electrode having
at least one edge that contacts the material of the support
element, at least one temperature sensing element carried by the
electrode adjacent to the at least one edge, and a controller
coupled to the temperature sensing element and the generator to
control the supply of ablation energy based, at least in part, upon
temperature sensed by the at least one temperature sensing
element.
26. A system for ablating body tissue comprising a generator for
supplying ablation energy, a support element made of a material
that does not conduct ablation energy, an electrode carried by the
support element for contact with tissue, the electrode being made
of a material that transmits ablation energy, the electrode having
opposed edges that contact the material of the support element,
temperature sensing elements carried by the electrode adjacent to
the opposed edges, and a controller coupled to the temperature
sensing elements and the generator to control the supply of
ablation energy based, at least in part, upon temperatures sensed
by the temperature sensing elements.
27. A system according to claim 26 wherein the controller includes
means for selecting a temperature sensed by one of the temperature
sensing elements that is higher than a temperature sensed by the
other temperature sensing element and for controlling the supply of
ablation energy based, at least in part, upon the selected
temperature.
28. A system for ablating body tissue comprising a generator for
supplying ablation energy, a support element made of a material
that does not conduct ablation energy, and an array of spaced apart
electrodes carried by the support element for contact with tissue,
each electrode being made of a material that transmits ablation
energy, each electrode having opposed edges that contact the
material of the support element, the array including a first
electrode that begins the array and a second electrode that ends
the array, first and second temperature sensing elements carried
by, respectively, the first and second electrodes adjacent to one
of their respective opposed edges, and a controller coupled to the
first and second temperature sensing elements and the generator to
control the supply of ablation energy to the array of electrodes
based, at least in part, upon temperatures sensed by the first and
second temperature sensing elements.
29. A method for ablating body tissue comprising the steps of
supplying ablation energy to an electrode carried by a support
element made of a material that does not conduct ablation energy,
the electrode having at least one edge that contacts the material
of the support element, sensing temperature with at least one
temperature sensing element carried by the electrode adjacent to
the at least one edge, and controlling the supply of ablation
energy based, at least in part, upon temperature sensed by the at
least one temperature sensing element.
30. A method for ablating body tissue comprising the steps of
supplying ablation energy to an electrode carried by a support
element made of a material that does not conduct ablation energy,
the electrode having opposed edges that contact the material of the
support element, sensing temperatures with temperature sensing
elements carried by the electrode adjacent to the opposed edges,
and controlling the supply of ablation energy based, at least in
part, upon temperatures sensed by the temperature sensing
elements.
31. A method according to claim 30 wherein, in controlling the
supply of ablation energy, a temperature sensed by one of the
temperature sensing elements is selected that is higher than a
temperature sensed by the other temperature sensing element and the
supply of ablation energy is controlled based, at least in part,
upon the selected temperature.
32. A method for ablating body tissue comprising the steps of
supplying ablation energy to an array of spaced apart electrodes
carried by a support element made of a material that does not
conduct ablation energy, each electrode in the array having opposed
edges that contact the material of the support element, the array
including a first electrode that begins the array and a second
electrode that ends the array, sensing temperatures with first and
second temperature sensing elements carried by, respectively, the
first and second electrodes adjacent to one of their respective
opposed edges, and controlling the supply of ablation energy to the
array of electrodes based, at least in part, upon temperatures
sensed by the first and second temperature sensing elements.
33. A device according to claim 1 or 2 or 3 or 4 wherein the
temperature sensing element is carried inside the electrode.
34. A device according to claim 1 or 2 or 3 or 4 wherein the
temperature sensing element is carried outside the electrode.
Description
RELATED CASES
[0001] This case is a continuation-in-part of U.S. application Ser.
No. 08/286,930, filed Aug. 8, 1994, entitled "Systems and Methods
for Controlling Tissue Ablation Using Multiple Temperature Sensing
Elements." This case is also a continuation-in-part of U.S.
application Ser. No. 08/287,192, filed Aug. 8, 1994, entitled
"Systems and Methods for Forming Elongated Lesion Patterns in Body
Tissue Using Straight of Curvilinear Electrode Elements."
FIELD OF THE INVENTION
[0002] The invention relates to systems and methods for ablating
myocardial tissue for the treatment of cardiac conditions.
BACKGROUND OF THE INVENTION
[0003] Physicians make use of catheters today in medical procedures
to gain access into interior regions of the body to ablate targeted
tissue areas. It is important for the physician to be able to
precisely locate the catheter and control its emission of energy
within the body during tissue ablation procedures.
[0004] For example, in electrophysiological therapy, ablation is
used to treat cardiac rhythm disturbances.
[0005] During these procedures, a physician steers a catheter
through a main vein or artery into the interior region of the heart
that is to be treated. The physician places an ablating element
carried on the catheter near the cardiac tissue that is to be
ablated. The physician directs energy from the ablating element to
ablate the tissue and form a lesion.
[0006] In electrophysiological therapy, there is a growing need for
ablating elements capable of providing lesions in heart tissue
having different geometries.
[0007] For example, it is believed the treatment of atrial
fibrillation requires the formation of long, thin lesions of
different curvilinear shapes in heart tissue. Such long, thin
lesion patterns require the deployment within the heart of flexible
ablating elements having multiple ablating regions. The formation
of these lesions by ablation can provide the same therapeutic
benefits that the complex suture patterns that the surgical maze
procedure presently provides, but without invasive, open heart
surgery.
[0008] As another example, it is believed that the treatment of
atrial flutter and ventricular tachycardia requires the formation
of relatively large and deep lesions patterns in heart tissue.
Merely providing "bigger" electrodes does not meet this need.
Catheters carrying large electrodes are difficult to introduce into
the heart and difficult to deploy in intimate contact with heart
tissue. However, by distributing the larger ablating mass required
for these electrodes among separate, multiple electrodes spaced
apart along a flexible body, these difficulties can be
overcome.
[0009] With larger and/or longer multiple electrode elements comes
the demand for more precise control of the ablating process. The
delivery of ablating energy must be governed to avoid incidences of
tissue damage and coagulum formation. The delivery of ablating
energy must also be carefully controlled to assure the formation of
uniform and continuous lesions, without hot spots and gaps forming
in the ablated tissue.
SUMMARY OF THE INVENTION
[0010] The invention provides device and methods for ablating body
tissue. The devices and methods include an electrode carried by a
support element made of a material that does not conduct tissue
ablation energy. The electrode is made of a material that transmits
ablation energy. The electrode has at least one edge that contacts
the material of the support element. The devices and methods also
include at least one temperature sensing element carried by the
electrode adjacent to the at least one edge.
[0011] Another aspect of the invention provides systems and methods
method for controlling the ablation of body tissue. The systems and
methods supply ablation energy to an electrode carried by a support
element made of a material that does not conduct ablation energy.
The electrode has at least one edge that contacts the material of
the support element. The systems and methods senses temperature
with at least one temperature sensing element carried by the
electrode adjacent to the at least one edge. The systems and
methods control the supply of ablation energy based, at least in
part, upon temperature sensed by the at least one temperature
sensing element.
[0012] The invention places the temperature sensing element in an
"edge region" between an electrode and a non-electrically
conducting support body. The edge region presents an area where
electrical conductivity is discontinuous. The resulting rise in
current density in this region generates localized increases in
power densities, and, therefore, it is a region where higher
temperatures are likely to exist. The invention places the
temperature sensing element just where localized "hot spots" are to
be expected. Reliable temperature sensing, which is sensitive to
variations in temperatures along the electrode, results.
[0013] Other features and advantages of the inventions are set
forth in the following Description and Drawings, as well as in the
appended Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1, is a view of a probe that carries a flexible
ablating element having multiple temperature sensing elements;
[0015] FIG. 2 is an enlarged view of the handle of the probe shown
in FIG. 1, with portions broken away and in section, showing the
steering mechanism for flexing the ablating element;
[0016] FIGS. 3 and 4 show the flexure of the ablating element
against different tissue surface contours;
[0017] FIG. 5 is a side view of a flexible ablating element
comprising a rigid tip electrode element and a rigid body electrode
segment;
[0018] FIG. 6 is a perspective view of a segmented flexible
electrode element, in which each electrode segment comprises a
wrapped wire coil;
[0019] FIGS. 7A/B are, respectively, side and side section views of
different wrapped wire coils comprising flexible electrode
elements;
[0020] FIGS. 8A/B are, respectively, a side and side section view
of multiple wrapped wire coils comprising a flexible electrode
element;
[0021] FIG. 9 is a side view of a flexible ablating element
comprising a rigid tip electrode element and a flexible body
electrode segment;
[0022] FIG. 10 is a perspective view of a continuous flexible
electrode element comprising a wrapped wire coil;
[0023] FIG. 11 is a perspective view of a continuous flexible
electrode element comprising a wrapped ribbon;
[0024] FIGS. 12A/B are views of a flexible ablating element
comprising a wrapped wire coil including a movable sheath for
changing the impedance of the coil and the ablating surface area
when in use;
[0025] FIG. 13 is an end section view of an ablating electrode
element carrying one temperature sensing element;
[0026] FIG. 14 is an end section view of an ablating electrode
element carrying two temperature sensing elements;
[0027] FIG. 15 is an end section view of an ablating electrode
element carrying three temperature sensing elements;
[0028] FIG. 16 is a side section view of a flexible ablating
element comprising multiple rigid electrode elements, showing one
manner of mounting at least one temperature sensing element beneath
the electrode elements;
[0029] FIG. 17 is a side section view of a flexible ablating
element comprising multiple rigid electrode elements, showing
another manner of mounting at least one temperature sensing element
between adjacent electrode elements;
[0030] FIG. 18 is a side section view of a flexible ablating
element comprising multiple rigid ablating elements, showing
another manner of mounting at least one temperature sensing element
on the electrode elements;
[0031] FIG. 19 is an enlarged top view of the mounting the
temperature sensing element on the rigid electrode shown in FIG.
18;
[0032] FIGS. 20 and 21 are side section views of the mounting of
temperature sensing elements on the ablating element shown in FIG.
5;
[0033] FIG. 22 is a view of a flexible ablating element comprising
a continuous wrapped coil, showing one manner of mounting
temperature sensing elements along the length of the coil;
[0034] FIG. 23 is a view of a flexible ablating element comprising
a continuous wrapped coil, showing another manner of mounting
temperature sensing elements along the length of the coil;
[0035] FIG. 24 is an enlarged view of the mounting of the
temperature sensing element on the coil electrode shown in FIG.
23;
[0036] FIG. 25 is a view of a flexible ablating element comprising
a continuous wrapped ribbon, showing a manner of mounting
temperature sensing elements along the length of the ribbon;
[0037] FIG. 26 is a side section view of a large electrode with
temperature sensing elements positioned at its edges;
[0038] FIG. 27 is a perspective view of an array of long electrodes
with temperature sensing elements position at each long electrode
edge and in between each long electrode;
[0039] FIG. 28 is a side section view of an array of short
electrodes, each one carrying a temperature sensing element at one
edge;
[0040] FIG. 29 is a side view of an array of short electrodes, with
temperature sensing elements position at the edge of the short
electrodes beginning and ending the array, as well in the middle of
each intermediate short electrode;
[0041] FIGS. 30 and 31 are schematic views of a system for
controlling the application of ablating energy to multiple
electrodes using multiple temperature sensing inputs;
[0042] FIG. 32 is a schematic flow chart showing an implementation
of the temperature feedback controller shown in FIGS. 30 and 31,
using individual amplitude control with collective duty cycle
control; and
[0043] FIG. 33 is a schematic view of a neural network predictor,
which receives as input the temperatures sensed by multiple sensing
elements at a given electrode region and outputs a predicted
temperature of the hottest tissue region.
[0044] The invention may be embodied in several forms without
departing from its spirit or essential characteristics. The scope
of the invention is defined in the appended claims, rather than in
the specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] This Specification discloses multiple electrode structures
that embody aspects the invention. This Specification also
discloses tissue ablation systems and techniques using multiple
temperature sensing elements that embody other aspects of the
invention. The illustrated and preferred embodiments discuss these
structures, systems, and techniques in the context of
catheter-based cardiac ablation. That is because these structures,
systems, and techniques are well suited for use in the field of
cardiac ablation.
[0046] Still, it should be appreciated that the invention is
applicable for use in other tissue ablation applications. For
example, the various aspects of the invention have application in
procedures for ablating tissue in the prostrate, brain, gall
bladder, uterus, and other regions of the body, using systems that
are not necessarily catheter-based.
[0047] I. Flexible Ablating Elements
[0048] FIG. 1 shows a flexible ablating element 10 for making
lesions within the heart.
[0049] The element 10 is carried at the distal end of a catheter
body 12 of an ablating probe 14. The ablating probe 14 includes a
handle 16 at the proximal end of the catheter body 12. The handle
16 and catheter body 12 carry a steering mechanism 18 for
selectively bending or flexing the ablating element 10 in two
opposite directions, as the arrows in FIG. 1 show.
[0050] The steering mechanism 18 can vary. In the illustrated
embodiment (see FIG. 2), the steering mechanism 18 includes a
rotating cam wheel 20 with an external steering lever 22 (see FIG.
1). As FIG. 2 shows, the cam wheel 20 holds the proximal ends of
right and left steering wires 24. The wires 24 pass through the
catheter body 12 and connect to the left and right sides of a
resilient bendable wire or spring 26 (best shown in FIGS. 20 and
23) enclosed within a tube 28 inside the ablating element 10.
[0051] Further details of this and other types of steering
mechanisms for the ablating element 10 are shown in Lundquist and
Thompson U.S. Pat. No. 5,254,088, which is incorporated into this
Specification by reference.
[0052] As FIG. 1 shows, forward movement of the steering lever 22
flexes or curves the ablating element 10 down. Rearward movement of
the steering lever 22 flexes or curves the ablating element 10
up.
[0053] Various access techniques can be used to introduce the probe
14 into the desired region of the heart. For example, to enter the
right atrium, the physician can direct the probe 14 through a
conventional vascular introducer through the femoral vein. For
entry into the left atrium, the physician can direct the probe 14
through a conventional vascular introducer retrograde through the
aortic and mitral valves.
[0054] Alternatively, the physician can use the delivery system
shown in pending U.S. application Ser. No. 08/033,641, filed Mar.
16, 1993, and entitled "Systems and Methods Using Guide Sheaths for
Introducing, Deploying, and Stabilizing Cardiac Mapping and
Ablation Probes."
[0055] The physician can verify intimate contact between the
element 10 and heart tissue using conventional pacing and sensing
techniques. Once the physician establishes intimate contact with
tissue in the desired heart region, the physician applies ablating
energy to the element 10. The type of ablating energy delivered to
the element 10 can vary. In the illustrated and preferred
embodiment, the element 10 transmits electromagnetic radio
frequency energy.
[0056] The flexible ablating element 10 can be configured in
various ways. With these different configurations, the flexible
ablating element can form lesions of different characteristics,
from long and thin to large and deep in shape.
[0057] a. Segmented, Rigid Electrode Elements
[0058] FIGS. 3 and 4 show one implementation of a preferred type of
flexible ablating element, designated 10(1). The element 10(1)
includes multiple, generally rigid electrode elements 30 arranged
in a spaced apart, segmented relationship upon a flexible body
32.
[0059] The flexible body 32 is made of a polymeric, electrically
nonconductive material, like polyethylene or polyurethane. The body
32 carries within it the resilient bendable wire or spring with
attached steering wires (best shown in FIGS. 20 and 23), so it can
be flexed to assume various curvilinear shapes.
[0060] The segmented electrodes 30 comprise solid rings of
conductive material, like platinum. The electrode rings 30 are
pressure fitted about the body 32. The flexible portions of the
body 32 between the rings 30 comprise electrically nonconductive
regions.
[0061] The body 32 can be flexed between the spaced apart
electrodes 30 to bring the electrode 30 into intimate contact along
a curvilinear surface of the heart wall, whether the heart surface
curves outward (as FIG. 3 shows) or curves inward (as FIG. 4
shows).
[0062] FIG. 5 shows an implementation of another preferred type of
a flexible ablating element, of the same general style as element
10(1), designated 10(2). Element 10(2) includes two generally rigid
electrode elements 34 and 36 arranged in a spaced apart
relationship at the distal tip of a flexible body 38. The flexible
body 38 is made of electrically insulating material, like
polyurethane and PEBAX.RTM. plastic material. The body 38 carries
one relatively large, rigid metal electrode 34 at its tip, which
comprises a body of electrically conductive material, like
platinum. The body 38 also carries another rigid electrode 36,
which comprises a solid ring 36 of electrically conductive
material, like platinum, pressure fitted about the body 38. As FIG.
5 shows, the ablating element 10(2) can also include one or more
conventional sensing ring electrodes 40 proximally spaced from the
ablating ring electrode 36. The sensing ring electrodes 40 serve to
sense electrical events in heart tissue to aid the physician in
locating the appropriate ablation site.
[0063] As shown in phantom lines in FIG. 5, the flexible body 38,
when pressed against the endocardial surface targeted for ablation,
bends to place the sides of the rigid electrodes 34 and 36 in
intimate contact against the particular contour of the surface. The
flexible nature of the ablating element 10(2) can be further
augmented by the inclusion of the resilient bendable wire or spring
26 within it (best shown in FIG. 20). In this embodiment, the
steering wires 24 connect to the left and right sides of the
bendable wire 26. The opposite ends of the steering wires 24
connect to a steering mechanism of the type previously described
and shown in FIG. 2. In this arrangement, the physician can use the
steering mechanism to remotely flex the electrodes 34 and 36 in the
manner shown in FIG. 5.
[0064] Preferably, as FIG. 20 shows, the steering wires 24 are
secured to the bendable wire 26 near its distal end, where the
bendable wire 26 is itself secured to the tip electrode 34. Bending
of the wire 26 thereby directly translates into significant
relative flexing of the distal end of the catheter body 38, which
carries the electrodes 34 and 36.
[0065] Alternatively, the region between the electrodes 34 and 36
can be stiff, not flexible. In this arrangement, pressing the 34
and 36 against tissue brings the tissue into conformance about the
electrodes 34 and 36.
[0066] The generally rigid, segmented electrodes 30 in element
10(1) and 34/36 in element 10(2) can be operated, at the
physician's choice, either in a unipolar ablation mode or in a
bipolar mode. In the unipolar mode, ablating energy is emitted
between one or more the electrodes 30 (in element 10(1)) or
electrodes 34/36 (in element 10(2)) and an external indifferent
electrode. In the bipolar mode, ablating energy is emitted between
two of the electrodes 30 (in element 10(1)) or the electrodes 34
and 36 (in element 10(2)), requiring no external indifferent
electrode.
[0067] B. Flexible Electrode Elements
[0068] FIG. 6 shows an implementation of another preferred style of
a flexible ablating element, designated 10(3). The element 10(3),
unlike elements 10(1) and 10(2), includes generally flexible
electrode elements 44 carried on a likewise flexible body 42.
[0069] The flexible body 42 is made of a polymeric, electrically
nonconductive material, like polyethylene or polyurethane, as the
flexible body of elements 10(1) and 10(2). The body 42 also
preferably carries within it the resilient bendable wire or spring
26 with attached steering wires 24 (best shown in FIGS. 29 and 30),
so it can be flexed to assumed various curvilinear shapes, as FIG.
6 shows.
[0070] The body 32 carries on its exterior surface an array of
segmented, generally flexible electrodes 44 comprising spaced apart
lengths of closely wound, spiral coils. The coil electrodes 44 are
made of electrically conducting material, like copper alloy,
platinum, or stainless steel. The electrically conducting material
of the coil electrode 44 can be further coated with
platinum-iridium or gold to improve its conduction properties and
biocompatibility.
[0071] The coils 44 can be made of generally cylindrical wire, as
the coil 44(a) shown in FIGS. 7A/B. Alternatively, the wire forming
the coils 44 can be non-circular in cross section. The wire, for
example, have a polygon or rectangular shape, as the coil 44(b)
shown in FIGS. 7A/B. The wire can also have a configuration in
which adjacent turns of the coil nest together, as the coil 44(c)
shown in FIGS. 7A/B. Coils 44(b) and 44(c) in FIGS. 7A/B present a
virtually planar tissue-contacting surface, which emulates the
tissue surface contact of the generally rigid electrode 30 shown in
FIGS. 3 and 4. However, unlike the electrode 30, the coils 44(b)
and 44(c), as well as the cylindrical coil 44(a), are each
inherently flexible and thereby better able to conform to the
surface contour of the tissue.
[0072] In another alternative arrangement, each coil 44 can
comprise multiple, counter wound layers of wire, as the coil 44(d)
shown in FIGS. 8A/B. This enhances the energy emitting capacity of
the coil 44(d), without significantly detracting from its inherent
flexible nature. The multiple layer coil 44(d) structure can also
be formed by using a braided wire material (not shown).
[0073] An alternative arrangement (shown in FIG. 9) uses the
generally rigid tip electrode 34 (like that in element 10(2), shown
in FIG. 5) in combination with a generally flexible electrode
segment 44 made of a closely wound coil. Of course, the tip
electrode 34, too, could comprise a generally flexible electrode
structure made of a closely wound coil. It should be apparent by
now that many combinations of rigid and flexible electrode
structures can be used in creating a flexible ablating element.
[0074] Furthermore, the inherent flexible nature of a coiled
electrode structures 44 makes possible the construction of a
flexible ablating element (designated 10(4) in FIG. 10) comprising
a continuous elongated flexible electrode 46 carried by a flexible
body 48. The continuous flexible electrode 46 comprises an
elongated, closely wound, spiral coil of electrically conducting
material, like copper alloy, platinum, or stainless steel, wrapped
about the flexible body. For better adherence, an undercoating of
nickel or titanium can be applied to the underlying flexible body.
The continuous coil electrode 46 can be arranged and configured in
the same fashion as the segmented coil electrodes 44 shown in FIGS.
7A/B and 8A/B.
[0075] The continuous coil electrode 46 is flexible and flexes with
the underlying body 48, as FIG. 10 shows. It can be easily placed
and maintained in intimate contact against heart tissue. The
continuous flexible coil structure shown in FIG. 10 therefore makes
possible a longer, flexible ablating element.
[0076] In an alternative arrangement (shown in FIGS. 12A/B), the
elongated coil electrode 46 can include a sliding sheath 50 made of
an electrically nonconducting material, like polyamide a stylet
(not shown) attached to the sheath 50 extends through the
associated catheter body 12 to a sliding control lever carried on
the probe handle 16 (also not shown). Moving the sheath 50 varies
the impedance of the coil electrode 46. It also changes the surface
area of the element 10(4).
[0077] Further details of this embodiment can be found in copending
U.S. patent application Ser. No. 08/137,576, filed Oct. 15, 1993,
and entitled "Helically Wound Radio Frequency Emitting Electrodes
for Creating Lesions in Body Tissue," which is incorporated into
this Specification by reference.
[0078] FIG. 11 shows another implementation of a generally flexible
element, designated element 10(5). The element 10(5) comprises a
ribbon 52 of electrically conductive material wrapped about a
flexible body 54. The ribbon 52 forms a continuous, inherently
flexible electrode element.
[0079] Alternatively, the flexible electrodes can be applied on the
flexible body by coating the body with a conductive material, like
platinum-iridium or gold, using conventional coating techniques or
an ion beam assisted deposition (IBAD) process. For better
adherence, an undercoating of nickel or titanium can be applied.
The electrode coating can be applied either as discrete, closely
spaced segments (to create an element like 10(3)) or in a single
elongated section (to create an element like 10(4) or 10(5)).
[0080] The flexible electrodes of elements 10(1) to 10(5) can be
operated, at the physician's choice, either in a unipolar ablation
mode or in a bipolar mode.
[0081] The ablating elements 10(1) to 10(5), as described above,
are infinitely versatile in meeting diverse tissue ablation
criteria.
[0082] For example, the ablating elements 10(1) and 10(3) to 10(5)
can be conditioned to form different configurations of elongated
(i.e., generally long and thin) lesion patterns. These elongated
lesion patterns can be continuous and extend along a straight line
or along a curve. Alternatively, these elongated lesion patterns
can be segmented, or interrupted, and extend along a straight line
or along a curve. Elongated lesion patterns can be used to treat,
for example, atrial fibrillation.
[0083] Alternatively, the ablating elements 10(1) to 10(5) can be
conditioned to form larger and deeper lesions in the heart. These
lesion large and deep lesion patterns can be used to treat, for
example, atrial flutter or ventricular tachycardia.
[0084] Various ways to control the characteristics of lesions
formed by the ablating elements 10(1) to 10(5) are disclosed in
detail in U.S. application Ser. No. 08/287,192, filed Aug. 8, 1994,
entitled "Systems and Methods for Forming Elongated Lesion Patterns
in Body Tissue Using Straight or Curvilinear Electrode
Elements."
[0085] II. Temperature Sensing
[0086] In the illustrated and preferred embodiments, each flexible
ablating element 10(1) to 10(5) carries at least one and,
preferably, at least two, temperature sensing element 80. The
multiple temperature sensing elements 80 measure temperatures along
the length of the element 10.
[0087] a. Temperature Sensing with Rigid Electrode Elements
[0088] In the segmented element 10(1) (see FIGS. 3 and 4), each
electrode segment 30 preferably carries at least one temperature
sensing element 80. In this configuration, the sensing elements 80
are preferably located in an aligned relationship along one side of
each segmented electrode 30, as FIGS. 3 and 4 show.
[0089] The body 32 preferably carries a fluoroscopic marker (like
the stripe 82 shown in FIGS. 3 and 4) for orientation purposes. The
stripe 82 can be made of a material, like tungsten or barium
sulfate, which is extruded into the tubing 12. The extruded stripe
can be fully enclosed by the tubing or it can be extruded on the
outer diameter of the tubing making it visible to the eye. FIG. 5
shows the marker in the wall of the tubing 12. An alternative
embodiment can be a fluoro-opaque wire like platinum or gold which
can be extruded into the tubing wall. Yet another embodiment is to
affix a marker in the inner diameter of the tubing during
manufacturing.
[0090] The sensing elements 80 can be on the same side as the
fluoroscopic marker 82 (as FIGS. 3 and 4 show), or on the opposite
side, as long as the physician is aware of the relative position of
them. Aided by the marker 82, the physician orients the element
10(1) so that the temperature sensing elements 80 contact the
targeted tissue.
[0091] Alternatively, or in combination with the fluoroscopic
marker 82, the sensing elements 80 can be consistently located on
the inside or outside surface of element 10(1) when flexed in a
given direction, up or down. For example, as FIG. 3 shows, when the
element 10(1) is flexed to the down, the sensing elements 80 are
exposed on the inside surface of the element 10(1). As FIG. 4
shows, when the element 10(1) flexed to the upward, the sensing
elements 80 are exposed on the outside surface of the element
10(1).
[0092] Each electrode segment 30 can carry more than a single
temperature sensing element 80. As FIGS. 13 to 15 show, each
electrode segment 30 can carry one, two, three, or more
circumferentially spaced apart temperature sensing elements 80. The
presence of multiple temperature sensing elements 80 on a single
electrode segment 30 gives the physician greater latitude in
positioning the ablating element 10(1), while still providing
temperature monitoring.
[0093] As FIG. 13 shows, a mask coating 56 of an electrically and
thermally insulating material can also be applied to the side of
the single sensor-segmented electrode 30 opposite to the
temperature sensing element 80, which, in use, is exposed to the
blood pool. As FIG. 14 shows, the mask coating 56 lies between the
two sensors 80 on the bi-directional segmented electrode 30. The
mask coating 56 minimizes the convective cooling effects of the
blood pool upon the regions of the electrode segment 80 that are
exposed to it. The temperature condition sensed by the element 80
facing tissue is thereby more accurate. When more than two
temperature sensors 80 are used on a given electrode segment 30,
masking becomes less advisable, as it reduces the effective surface
of the electrode segment 30 available for tissue contact and
ablation.
[0094] The temperature sensing elements 80 can comprise thermistors
or thermocouples. When using thermocouples as the sensing elements
80, a reference or cold junction thermocouple must be employed,
which is exposed to a known temperature condition. The reference
thermocouple can be placed within the temperature processing
element itself. Alternatively, the reference thermocouple can be
placed within the handle 18 of the catheter probe 14.
[0095] Further details regarding the use of thermocouples can be
found in a publication available from Omega, entitled Temperature,
pages T-7 to T-18. Furthermore, details of the use of multiple
thermocouples as temperature sensing elements 80 in tissue ablation
can be found in copending patent application Ser. No. 08/286,937,
filed Aug. 8, 1994, entitled "Systems and Methods for Sensing
Temperature Within the Body."
[0096] The sensing element or elements 80 can be attached on or
near the segmented electrodes 30 in various way.
[0097] For example, as FIG. 16 shows for the element 10(1), each
sensing element 80 is sandwiched between the exterior of the
flexible body 32 and the underside of the associated rigid
electrode segment 30. In the illustrated embodiment, the sensing
elements 80 comprise thermistors. The body 32 is flexible enough to
fit the sensing element 80 beneath the electrode segment 30. The
plastic memory of the body 32 maintains sufficient pressure against
the temperature sensing element 80 to establish good thermal
conductive contact between it and the electrode segment 30.
[0098] In an alternative embodiment (as FIG. 17 shows), the
temperature sensing element 80 is located between adjacent
electrode segments 30. In this arrangement, each sensing element 80
is threaded through the flexible body 32 between adjacent electrode
segments 30. In the illustrated embodiment, the temperature sensing
elements 80 comprise thermocouples. When the sensing element 80
comprises a thermocouple, an epoxy material 46, such as Master Bond
Polymer System EP32HT (Master Bond Inc., Hackensack, N.J.),
encapsulates the thermocouple junction 84, securing it to the
flexible body 32. Alternatively, the thermocouple junction 84 can
be coated in a thin layer of polytetrafluoroethylene (PTFE)
material. When used in thicknesses of less than about 0.002 inch,
these materials have the sufficient insulating properties to
electrically insulate the thermocouple junction 84 from the
associated electrode segment 30, while providing sufficient
thermally conducting properties to establish thermal conductive
contact with electrode segment 30. The use of such materials
typically will not be necessary when thermistors are used, because
conventional thermistors are already encapsulated in an
electrically insulating and thermally conducting material.
[0099] In another alternative embodiment (as FIGS. 18 and 19 show),
the temperature sensing element 80 physically projects through an
opening 86 in each electrode segment 30. As in the embodiment shown
in FIG. 17, the sensing elements 80 comprise thermocouples, and a
thermally conducting and electrically insulating epoxy material
encapsulates the thermocouple junction 84, securing it within the
opening 86.
[0100] It should be appreciated that some sensing elements 80 can
be carried by the electrode segments 30, while other sensing
elements 80 can be carried between the element segments 30. Many
combinations of sensing element locations are possible, depending
upon particular requirements of the ablating procedure.
[0101] In the element 10(2) (see FIG. 20), each electrode segment
34 and 36 carries at least one temperature sensing element 80. In
the illustrated embodiment, the sensing element 80 comprises a
thermistor.
[0102] The tip electrode segment 34 carries a temperature sensing
element 80 within a cavity 88 drilled along its axis. The body
electrode segment 36 also carries at least one temperature sensing
element 80, which is sandwiched beneath the electrode segment 36
and the flexible body 38, in the manner previously described and
shown in FIG. 16. The sensing element 80 in the electrode segment
36 can be alternatively secured in the manners previously described
and shown in FIGS. 17 and 18. Alternatively, as earlier described,
the side of the electrode segment 36 opposite to the single sensing
temperature element 80 can carrying the mask coating 56.
[0103] As shown in FIG. 21, either or both electrodes 34 and 36 of
element 10(2) can carry more than one temperature sensing element
80. In this arrangement, the tip electrode 34 carries additional
temperature sensing elements 80 in side cavities 90 that extend at
angles radially from the axis of the electrode 34. The body
electrode segment 36 carries additional sensing elements 80 in the
manner shown in FIGS. 14 and 15.
[0104] As the diameter of the electrodes 34 and 36 increases, the
use of multiple temperature sensing elements 80 becomes more
preferred. The multiple sensing elements 80 are circumferentially
spaced to assure that at least one element 80 is in thermal
conductive contact with the same tissue area as the associated
electrode 34 or 36.
[0105] B. Temperature Sensing with Flexible Electrode Elements
[0106] In the flexible electrode elements 10(3) and 10(4) (earlier
shown in FIGS. 6 and 10), the multiple temperature sensing elements
80 are preferably located at or near the electrical connection
points between the wires 58 and the coil electrode segments 44 or
continuous coil electrode 46, as FIGS. 22 and 23 best show. This
location for the temperature sensing elements 80 is preferred
because higher temperatures are typically encountered at these
connection points along the coil electrode 44 or 46.
[0107] As FIG. 22 shows, the sensing elements 80 can be secured to
the inside surface of the coil electrode 44 or 46. Alternatively,
the sensing elements 80 can be sandwiched between the inside
surface of the electrode 44 or 46 and an underlying flexible body,
as FIGS. 15A/B show. In FIGS. 15A/B and 29, the sensing elements 80
comprise thermistors.
[0108] Alternatively, as FIGS. 23 and 24 show, the sensing elements
80 can be threaded up through the windings in the coil electrode 44
or 46 to lay upon its exterior surface. In the illustrated
embodiment, the sensing elements 80 comprise thermocouples, and the
thermocouple junction 84 is encapsulated in on an epoxy or PTFE
coating, as previously described.
[0109] When the elongated electrode 46 includes a sliding sheath 50
see FIGS. 12A/B), the movable sheath 50 carries, in addition to the
temperature sensing elements 80 spaced along the length of the coil
electrode 56, another temperature sensing element 80 at its distal
end.
[0110] In the case of flexible electrode element 10(5) (earlier
shown in FIG. 11), the sensing elements 80 are sandwiched between
the wrapped ribbon 52 and the underlying flexible body 54, as FIG.
25 shows. In the illustrated embodiment, the sensing elements 80
comprise thermocouples having junctions 84 encapsulated in an
electrically insulating and thermally conducting coating.
[0111] C. Location of Temperature Sensing Elements
[0112] The positioning of the temperature sensing elements 80 on
the electrode elements is important for achieving reliable
temperature sensing, particularly when the length of an individual
electrode on the element 80 exceeds about 10 mm, or when the
element 10 comprises arrays of shorter, segmented electrodes.
Without proper placement of the temperature sensor elements 80
under these circumstances, variations in tissue temperature, and in
particular the presence of "hot spots," can go undetected. Also,
with predetermined placement of the temperature sensing elements,
temperature gradients along the element 10 can be obtained for
ablation control purposes.
[0113] Electrode elements having lengths exceeding about 10 mm will
be called "long" electrodes, which is identified by the numeral 100
in FIG. 26. The elongated coil electrode 46 shown in FIG. 10
exemplifies a typical long electrode. FIGS. 6 and 9 also show an
arrangement in which each coil electrode segment 44 could comprise
a long electrode.
[0114] As FIG. 26 shows, in a preferred embodiment, the temperature
sensing elements 80 are preferably located at the edges 102 and 104
of the long electrode 100. The edges 102 and 104 are where the
electrode 100 abuts the underlying, non-electrically-conductive
support body 106. RF current densities are high at these edges 102
and 104, because the edges 102 and 104 are regions where electrical
conductivity is discontinuous. The resulting rise in current
density at the electrode edges 102 and 104 generates localized
regions of increased power density and, therefore, regions where
higher temperatures exist. In long electrode elements 100,
temperature sensing elements 80 should preferably be located in
these edge regions where high localized temperatures are to be
expected.
[0115] Most preferably, as FIG. 26 shows, two temperature sensing
elements 80 should be located on each long electrode 100, with the
temperature sensing elements 80 positioned in oppositely spaced
relationship on each edge 102 and 104 of the long electrode
100.
[0116] When sequences of long electrodes 100 are used (see FIG.
27), an additional temperature sensing element 80 should also
preferably be located in between adjacent long electrodes 100. When
positioned in this way, the temperature sensing elements 80 can
acquire temperature gradients along the entire electrode element
10, which can be used to control the application of ablation
energy, as will be described later.
[0117] The use of multiple temperature sensing elements 80 on
opposite sides of long electrode 100 also reduces the sensitivity
of temperature control to poor electrode contact with tissue, and
also reduces errors should one or more temperature sensing elements
face blood instead of tissue. This is because the probability of at
least one sensor facing the tissue is increased.
[0118] Electrode elements having lengths less than about 10 mm will
be called "short" electrodes, which are identified by the numeral
110 in FIG. 28. The segmented electrodes 30 shown in FIG. 3
exemplify a typical sequence of short electrodes. FIGS. 6 and 9
also show an arrangement in which each coil electrode segment 44
could comprise a short electrode.
[0119] When sequences of short electrodes 110 are used (see FIG.
28), the temperature sensing elements 80 are also preferable
located at one edge 112 of each short electrode 110, for the same
reasons explained above in connection with long electrodes 100.
Still, when the electrodes 110 are very short (for example, less
than about 5 mm) (see FIG. 29), a centrally located temperature
sensing element 80 can be used (as FIGS. 3 and 18 also show, for
example). In this arrangement (see FIG. 29), the short electrodes
110 that begin and end the electrode sequence should preferably
carry temperature sensing elements 80 located at their edges 112.
In such an arrangement (as FIG. 29 also shows), it is also
preferable to locate additional temperature sensing elements 80
generally midway between adjacent short electrodes 110. The
temperature sensing elements 80 are thereby positioned to obtain
temperature gradients along the entire length of the electrode
element 10.
[0120] III. Control of Cardiac Ablation Using Multiple Temperature
Feedback Control
[0121] FIG. 30 shows, in schematic form, a representative system
200 for applying ablating energy by multiple emitters based, at
least in part, upon local temperature conditions sensed by multiple
sensing elements 80.
[0122] In FIG. 30, the multiple sensing elements 80 comprise
thermocouples 208, 209, and 210 individually associated with the
multiple emitters of ablating energy, which comprise electrode
regions 201, 202, and 203. The system 200 also includes a common
reference thermocouple 211 carried within the coupler element 211
for exposure to the blood pool. Alternatively, other kinds of
temperature sensing elements can be used, like, for example,
thermistors, fluoroptic sensors, and resistive temperature sensors,
in which case the reference sensor 211 would typically not be
required.
[0123] The system 200 further includes an indifferent electrode 219
for operation in a uni-polar mode.
[0124] The ablating energy emitters 201, 202, 203 can comprise the
rigid electrode segments 30 previously described. Alternatively,
the electrode regions 201, 202, 203 can comprise a continuous or
segmented flexible electrode of wrapped wire or ribbon. It should
be appreciated that the system 200 can be used in association with
any ablating element that employs multiple, independently actuated
ablating elements.
[0125] The system 200 includes a source 217 of ablating energy. In
FIG. 30, the source 217 generates radio frequency (RF) energy. The
source 217 is connected (through a conventional isolated output
stage 216) to an array of power switches 214, one for each
electrode region 201, 202, and 203. A connector 212 (carried by the
probe handle) electrically couples each electrode region 201, 203,
203 to its own power switch 214 and to other parts of the system
200.
[0126] The system 200 also includes a microcontroller 231 coupled
via an interface 230 to each power switch 214. The microcontroller
231 turns a given power switch 214 on or off to deliver RF power
from the source 217 individually to the electrode regions 201, 202,
and 203. The delivered RF energy flows from the respective
electrode region 201, 202, and 203, through tissue, to the
indifferent electrode 219, which is connected to the return path of
the isolated output stage 216.
[0127] The power switch 214 and interface 230 configuration can
vary according to the type of ablating energy being applied. FIG.
31 shows a representative implementation for applying RF ablating
energy.
[0128] In this implementation, each power switch 214 includes an
N-MOS power transistor 235 and a P-MOS power transistor 236 coupled
in between the respective electrode region 201, 202, and 203 and
the isolated output stage 216 of the power source 217.
[0129] A diode 233 conveys the positive phase of RF ablating energy
to the electrode region. A diode 234 conveys the negative phase of
the RF ablating energy to the electrode region. Resistors 237 and
238 bias the N-MOS and P-MOS power transistors 235 and 236 in
conventional fashion.
[0130] The interface 230 for each power switch 214 includes two NPN
transistors 239 and 240. The emitter of the NPN transistor 239 is
coupled to the gate of the N-MOS power transistor 235. The
collector of the NPN transistor 240 is coupled to the gate of the
P-MOS power transistor 280.
[0131] The interface for each power switch 214 also includes a
control bus 243 coupled to the microcontroller 231. The control bus
243 connects each power switch 214 to digital ground (DGND) of the
microcontroller 231. The control bus 243 also includes a (+) power
line (+5V) connected to the collector of the NPN transistor 239 and
a (-) power line (-5V) connected to the emitter of the NPN
interface transistor 240.
[0132] The control bus 243 for each power switch 214 further
includes an E.sub.SEL line. The base of the NPN transistor 239 is
coupled to the E.sub.SEL line of the control bus 243. The base of
the NPN transistor 240 is also coupled the E.sub.SEL line of the
control bus 243 via the Zener diode 241 and a resistor 232.
E.sub.SEL line connects-to the cathode of the Zener diode 241
through the resistor 232. The Zener diode 241 is selected so that
the NPN transistor 240 turns on when E.sub.SEL exceeds about 3
volts (which, for the particular embodiment shown, is logic 1).
[0133] It should be appreciated that the interface 230 can be
designed to handle other logic level standards. In the particular
embodiment, it is designed to handle conventional TTL (transistor
transfer logic) levels.
[0134] The microcontroller 231 sets E.sub.SEL of the control bus
243 either at logic 1 or at logic 0. At logic 1, the gate of the
N-MOS transistor 235 is connected to (+) 5 volt line through the
NPN transistors 239. Similarly, the gate of the P-MOS transistor
236 is connected to the (-) 5 volt line through the NPN transistor
240. This conditions the power transistors 235 and 236 to conduct
RF voltage from the source 217 to the associated electrode region.
The power switch 214 is "on."
[0135] When the microcontroller 231 sets E.sub.SEL at logic 0, no
current flows through the NPN transistors 239 and 240. This
conditions the power transistors 235 and 236 to block the
conduction of RF voltage to the associated electrode region. The
power switch 214 is "off."
[0136] The system 200 (see FIG. 30) further includes two analog
multiplexers (MUX) 224 and 225. The multiplexers 224 and 225
receive voltage input from each thermocouple 208, 209, 210, and
211. The microcontroller 231 controls both multiplexers 224 and 225
to select voltage inputs from the multiple temperature sensing
thermocouples 208, 209, 210, and 211.
[0137] The voltage inputs from the thermocouples 208, 209, 210, and
211 are sent to front end signal conditioning electronics. The
inputs are amplified by differential amplifier 226, which reads the
voltage differences between the copper wires of the thermocouples
208/209/210 and the reference thermocouple 211. The voltage
differences are conditioned by element 227 and converted to digital
codes by the analog-to-digital converter 228. The look-up table 229
converts the digital codes to temperature codes. The temperature
codes are read by the microcontroller 231.
[0138] The microcontroller 231 compares the temperature codes for
each thermocouple 208, 209, and 210 to preselected criteria to
generate feedback signals. The preselected criteria are inputted
through a user interface 232. These feedback signals control the
interface power switches 214 via the interface 230, turning the
electrodes 201, 202, and 203 off and on.
[0139] The other multiplexer 225 connects the thermocouples 208,
209, 210, and 211 selected by the microcontroller 231 to a
temperature controller 215. The temperature controller 215 also
includes front end signal conditioning electronics, as already
described with reference to elements 226, 227, 228, and 229. These
electronics convert the voltage differences between the copper
wires of the thermocouples 208/209/210 and the reference
thermocouple 211 to temperature codes. The temperature codes are
read by the controller and compared to preselected criteria to
generate feedback signals. These feedback signals control the
amplitude of the voltage (or current) generated by the source 217
for delivery to the electrodes 201, 202, and 203.
[0140] Based upon the feedback signals of the microcontroller 231
and the temperature controller 215, the system 200 distributes
power to the multiple electrode regions 201, 202, and 203 to
establish and maintain a uniform distribution of temperatures along
the ablating element. In this way, the system 200 obtains safe and
efficacious lesion formation using multiple emitters of ablating
energy.
[0141] The system 200 can control the delivery of ablating energy
in different ways. Representative modes will now be described.
[0142] Individual Amplitudes/Collective Duty Cycle
[0143] The electrode regions 201, 202, and 203 will be symbolically
designated E(J), where J represents a given electrode region (J=1
to N).
[0144] As before described, each electrode region E(J) has at least
one temperature sensing element 208, 209, and 210, which will be
designated S(J, K), where J represents the electrode region and K
represents the number of temperature sensing elements on each
electrode region (K=1 to M).
[0145] In this mode (see FIG. 32), the microcontroller 316 operates
the power switch interface 230 to deliver RF power from the source
217 in multiple pulses of duty cycle 1/N.
[0146] With pulsed power delivery, the amount of power (P.sub.E(J))
conveyed to each individual electrode region E(J) is expressed as
follows:
P.sub.E(J).about.AMP.sub.E(J).sup.2.times.DUTYCYCLE.sub.E(J)
[0147] where:
[0148] AMP.sub.E(J) is the amplitude of the RF voltage conveyed to
the electrode region E(J), and
[0149] DUTYCYCLE.sub.E(J) is the duty cycle of the pulse, expressed
as follows: 1 DUTYCYCLE E ( J ) = TON E ( J ) TON E ( J ) + TOFF E
( J )
[0150] where:
[0151] TON.sub.E(J) is the time that the electrode region E(J)
emits energy during each pulse period,
[0152] TOFF.sub.E(J) is the time that the electrode region E(J)
does not emit energy during each pulse period.
[0153] The expression TON.sub.E(J)+TOFF.sub.E(J) represents the
period of the pulse for each electrode region E(J).
[0154] In this mode, the microcontroller 231 collectively
establishes duty cycle (DUTYCYCLE.sub.E(J)) of 1/N for each
electrode region (N being equal to the number of electrode
regions).
[0155] The microcontroller 231 may sequence successive power pulses
to adjacent electrode regions so that the end of the duty cycle for
the preceding pulse overlaps slightly with the beginning of the
duty cycle for the next pulse. This overlap in pulse duty cycles
assures that the source 217 applies power continuously, with no
periods of interruption caused by open circuits during pulse
switching between successive electrode regions.
[0156] In this mode, the temperature controller 215 makes
individual adjustments to the amplitude of the RF voltage for each
electrode region (AMP.sub.E(J)), thereby individually changing the
power P.sub.E(J) of ablating energy conveyed during the duty cycle
to each electrode region, as controlled by the microcontroller
231.
[0157] In this mode, the microcontroller 231 cycles in successive
data acquisition sample periods. During each sample period, the
microcontroller 231 selects individual sensors S(J, K), and voltage
differences are read by the controller 215 (through MUX 225) and
converted to temperature codes TEMP(J).
[0158] When there is more than one sensing element associated with
a given electrode region (for example, when edge-located sensing
elements are used, as FIGS. 26 and 27 show), the controller 215
registers all sensed temperatures for the given electrode region
and selects among these the highest sensed temperature, which
constitutes TEMP(J).
[0159] In this mode, the controller 215 compares the temperature
TEMP(J) locally sensed at each electrode E(J) during each data
acquisition period to a set point temperature TEMP.sub.SET
established by the physician. Based upon this comparison, the
controller 215 varies the amplitude AMP.sub.E(J) of the RF voltage
delivered to the electrode region E(J), while the microcontroller
231 maintains the DUTYCYCLE.sub.E(J) for that electrode region and
all other electrode regions, to establish and maintain TEMP(J) at
the set point temperature TEMP.sub.SET.
[0160] The set point temperature TEMP.sub.SET can vary according to
the judgment of the physician and empirical data. A representative
set point temperature for cardiac ablation is believed to lie in
the range of 40.degree. C. to 95.degree. C., with 70.degree. C.
being a representative preferred value.
[0161] The manner in which the controller 215 governs AMP.sub.E(J)
can incorporate proportional control methods, proportional integral
derivative (PID) control methods, or fuzzy logic control
methods.
[0162] For example, using proportional control methods, if the
temperature sensed by the first sensing element
TEMP(1)>TEMP.sub.SET, the control signal generated by the
controller 215 individually reduces the amplitude AMP.sub.E(1) of
the RF voltage applied to the first electrode region E(1), while
the microcontroller 231 keeps the collective duty cycle
DUTYCYCLE.sub.E(1) for the first electrode region E(1) the same. If
the temperature sensed by the second sensing element
TEMP(2)<TEMP.sub.SET, the control signal of the controller 215
increases the amplitude AMP.sub.E(2) of the pulse applied to the
second electrode region E(2), while the microcontroller 231 keeps
the collective duty cycle DUTYCYCLE.sub.E(2) for the second
electrode region E(2) the same as DUTYCYCLE.sub.E(1), and so on. If
the temperature sensed by a given sensing element is at the set
point temperature TEMP.sub.SET, no change in RF voltage amplitude
is made for the associated electrode region.
[0163] The controller 215 continuously processes voltage difference
inputs during successive data acquisition periods to individually
adjust AMP.sub.E(J) at each electrode region E(J), while the
microcontroller 231 keeps the collective duty cycle the same for
all electrode regions E(J). In this way, the mode maintains a
desired uniformity of temperature along the length of the ablating
element.
[0164] Using a proportional integral differential (PID) control
technique, the controller 215 takes into account not only
instantaneous changes that occur in a given sample period, but also
changes that have occurred in previous sample periods and the rate
at which these changes are varying over time. Thus, using a PID
control technique, the controller 215 will respond differently to a
given proportionally large instantaneous difference between TEMP(J)
and TEMP.sub.SET, depending upon whether the difference is getting
larger or smaller, compared to previous instantaneous differences,
and whether the rate at which the difference is changing since
previous sample periods is increasing or decreasing.
[0165] Deriving Predicted Hottest Temperature
[0166] Because of the heat exchange between the tissue and the
electrode region, the temperature sensing elements may not measure
exactly the maximum temperature at the region. This is because the
region of hottest temperature occurs beneath the surface of the
tissue at a depth of about 0.5 to 2.0 mm from where the energy
emitting electrode region (and the associated sensing element)
contacts the tissue. If the power is applied to heat the tissue too
quickly, the actual maximum tissue temperature in this subsurface
region may exceed 100.degree. C. and lead to tissue desiccation
and/or micro-explosion.
[0167] FIG. 33 shows an implementation of a neural network
predictor 300, which receives as input the temperatures sensed by
multiple sensing elements S(J, K) at each electrode region, where J
represents a given electrode region (J=1 to N) and K represents the
number of temperature sensing elements on each electrode region
(K=1 to M). The predictor 300 outputs a predicted temperature of
the hottest tissue region T.sub.MAXPRED(t). The controller 215 and
microcontroller 231 derive the amplitude and duty cycle control
signals based upon T.sub.MAXPRED(t), in the same manners already
described using TEMP(J).
[0168] The predictor 300 uses a two-layer neural network, although
more hidden layers could be used. As shown in FIG. 32, the
predictor 300 includes a first and second hidden layers and four
neurons, designated N.sub.(L,X), where L identifies the layer 1 or
2 and X identifies a neuron on that layer. The first layer (L=1)
has three neurons (X=1 to 3), as follows N.sub.(1,1); N.sub.(1,2);
and N.sub.(1,3). The second layer (L=2) comprising one output
neuron (X=1), designated N.sub.(2,1).
[0169] Temperature readings from the multiple sensing elements,
only two of which--TS1(n) and TS2(n)--are shown for purposes of
illustration, are weighed and inputted to each neuron N.sub.(1,1);
N.sub.(1,2); and N.sub.(1,3) of the first layer. FIG. 33 represents
the weights as W.sup.L.sub.(K,N), where L=1; k is the input sensor
order; and N is the input neuron number 1, 2, or 3 of the first
layer.
[0170] The output neuron N.sub.(2,1) of the second layer receives
as inputs the weighted outputs of the neurons N.sub.(1,1);
N.sub.(1,2); and N.sub.(1,3). FIG. 32 represents the output weights
as W.sup.L.sub.(O,X), where L=2; O is the output neuron 1, 2, or 3
of the first layer; and X is the input neuron number of the second
layer. Based upon these weighted inputs, the output neuron
N.sub.(2,1) predicts T.sub.MAXPRED(t). Alternatively, a sequence of
past reading samples from each sensor could be used as input. By
doing this, a history term would contribute to the prediction of
the hottest tissue temperature.
[0171] The predictor 300 must be trained on a known set of data
containing the temperature of the sensing elements TS1 and TS2 and
the temperature of the hottest region, which have been previously
acquired experimentally. For example, using a back-propagation
model, the predictor 300 can be trained to predict the known
hottest temperature of the data set with the least mean square
error. Once the training phase is completed, the predictor 300 can
be used to predict T.sub.MAXPRED(t).
[0172] Other types of data processing techniques can be used to
derive T.sub.MAXPRED(t), See, e.g., copending patent application
Ser. No. 08/266,934, filed Jun. 27, 1994, and entitled "Tissue
Heating and Ablation Systems and Methods Using Predicted
Temperature for Monitoring and Control."
[0173] The illustrated and preferred embodiments use digital
processing controlled by a computer to analyze information and
generate feedback signals. It should be appreciated that other
logic control circuits using micro-switches, AND/OR gates,
invertors, analog circuits, and the like are equivalent to the
micro-processor controlled techniques shown in the preferred
embodiments.
[0174] Various features of the invention are set forth in the
following claims.
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